In automotive air conditioners, a variable capacity swash plate type compressor is known, which generally comprises a drive shaft, a rotor or lug plate mounted on and rotating with the drive shaft, and a swash plate. The swash plate is rotatably disposed on a spherical outer surface of a spherical sleeve member slidably mounted on the drive shaft. The compressor also includes a plurality of pistons each engaged with the swash plate via semi-spherical shoes.
Between the rotor and the swash plate is arranged a hinge mechanism which normally includes a first arm member projecting from the rotor in the rear direction of the compressor, a second arm member projecting from the swash plate in the front direction of the compressor, and a pin member connecting the first and second arm members through a pair of holes each formed in the respective arm members. One of the holes, for example, the hole formed in the rotor is elongated to guide the pin therein according to the change of inclination angle of the swash plate. The sliding motion of the pin within the elongated hole allows the change of inclination angle of the swash plate.
The hinge mechanism allows the swash plate to slide along and change its inclination angle with respect to the drive shaft. The hinge mechanism also allows the swash plate to rotate together with the drive shaft and the rotor. Rotation of the drive shaft causes the rotor and swash plate to rotate therewith, and accordingly, each piston engaged with the swash plate reciprocates within respective cylinder bores so that suction and compression of the refrigerant gas are completed. The capacity of the compressor is controlled by changing the inclination angle of the swash plate according to the pressure difference between the pressure in the crank chamber and the suction pressure.
In the above described variable capacity swash plate type compressor, the swash plate rotates with the drive shaft and nutates back and forth with respect to the rotor, and the rotation of the swash plate is converted into the reciprocation of the pistons within the respective cylinder bores. A suction force acts on the swash plate from the pistons during the suction stroke while a compression reaction force also acts on the swash plate from the pistons during the compression stroke. Therefore, the swash plate is subjected to a twisting motion or bending moment due to the suction and compression reaction forces acting from each piston on the swash plate. Moreover, since a torque exerted by the drive shaft is transmitted to the swash plate through the hinge mechanism, the swash plate is twisted with respect to the rotor in a direction different from the back and forth nutating motion.
As a solution for the above mentioned problems, U.S. Pat. No. 5,540,559 discloses a variable capacity compressor having an improved hinge unit. The hinge units comprise a pair of brackets protruding from the back surface of the rotary swash plate, a pair of guide pins each having one end fixed to each bracket and the other end fixed to a spherical element, and a pair of support arms protruding from the upper front surface of the rotor. Each support arm is provided with a circular guide hole into which the spherical element of the guide pin is rotatably and slidably inserted. U.S. Pat. No. 5,336,056 discloses a hinge means including two support arms extended axially rearwardly from the rotary support. Each of the support arms has a through-bore in which a race member is fixedly seated to turnably receive a ball element. Each ball element, too, has formed therein a through-hole operative as a guide hole permitting an axial slide of a guide pin therein. The guide pins are fixedly press-fitted in two through-bores formed in the rotary drive element of the swash plate assembly, respectively.
However, the hinge mechanisms disclosed in the above U.S. Patents are complex, and in particular, they require precise and time-consuming machining to form the circular guide holes and spherical elements of the guide pins in U.S. Pat. No. 5,540,559 and to form through-bores in U.S. Pat. No. 5,336,056. Moreover, to make that assembly symmetrical, the hinge mechanism including two support arms protruding from the rotor or the rotary drive element must be accurate and therefore is relatively burdensome. These raise the cost in manufacturing the compressor. Therefore, it is advantageous to provide a compressor with a hinge mechanism which is simple in its construction and machining thereof and prevents the twisting and bending of the swash plate.